1. Field of the Invention
The present invention relates to an infrared array sensor system, and more particularly to an infrared array sensor system having a simple and inexpensive construction capable of sensing the position and orientation of a human body as well as the presence and motion amount of the human body.
2. Description of the Prior Art
Generally, infrared sensors are classified into those of the pyroelectric type and those of the quantum efficiency type. Infrared sensors of the pyroelectric type are used to sense a human body and a motion amount of the human body by converting infrared rays emitted from the human body into heat. On the other hand, infrared sensors of the quantum efficiency type are mainly used for military purposes or to obtain infrared images in satellites because they have a superior sensitivity over the pyroelectric type infrared sensors.
Referring to FIG. 1, there is illustrated a conventional construction of a unit infrared sensor using a ceramic element.
The unit infrared sensor includes an infrared sensing chip 1 made of one of a PLZT-based pyroelectric ceramic, a single crystal such as LiTaO.sub.3 and a polyvinylidenedifluoride (PVDF) polymer. The chip 1 has an upper electrode as an infrared ray absorbing electrode and a lower electrode at its upper and lower surfaces, respectively. The chip 1 is supported by a support member 2 fixed on a stem 3 of a package, such as a TO-5 package, constituting a part of the unit infrared sensor. Formed on a predetermined portion of the support member 2 are a gate resistor Rg and a field effect transistor FET electrically connected to each other. The upper and lower electrodes of the chip 1 are connected to the gate resistor Rg and the field effect transistor FET by metal lines (not shown) extending in the support member 2.
Leads 4 extend through holes formed in the stem 3, respectively. The leads 4 are electrically connected to the field effect transistor (FET) and the gate resistor Rg, respectively. A metal housing 5 of the package is coupled to the stem 3 along the outer edge of the stem 3 so that the chip 1 is sealed from the outside of the package. A filter 6 adapted to transmit infrared rays of a band to be sensed is supported by the metal housing 5. The filter 6 is disposed at a position corresponding to the upper electrode of the chip 1.
Referring to FIG. 2, there is illustrated an equivalent circuit of the conventional unit infrared sensor having the above-mentioned construction. As shown in FIG. 2, the upper electrode of the chip 1 is connected to the gate of the FET receiving a voltage from a battery at its drain D. The lower electrode of the chip 1 is connected to a ground terminal G. The gate resistor Rg is connected between the gate of the transistor FET and the ground terminal G. On the other hand, a source resistor Rs is connected between the source S of the FET and the ground terminal G. A voltage Vs is generated across the source resistor Rs.
As a conventional infrared sensor mainly used in practical cases, an infrared sensor of the dual type is known. As shown in FIG. 3, the dual type infrared sensor includes a pyroelectric conductor having an upper electrode 8 divided into two electrodes to which leads 9 are electrically connected, respectively. Except for this construction, the dual type infrared sensor has the same construction as that of the unit infrared sensor of FIG. 1. That is, the dual type infrared sensor has the construction wherein a lower electrode 10 of the pyroelectric conductor is fixedly mounted to a support member 12 for the pyroelectric conductor by means of insulating adhesive 11.
Referring to FIG. 4, there is illustrated an equivalent circuit of the dual type infrared sensor having the above-mentioned construction. As shown in FIG. 4, the equivalent circuit of the dual type infrared sensor has a construction very similar to that of the equivalent circuit of FIG. 2 except that two pyroelectric chips having opposite polarization directions are connected in series.
Operation of the dual type infrared sensor will be described in conjunction with FIG. 7.
When the infrared sensor element 30 of the sensing unit 20 senses a motion of an object and thereby outputs an electrical signal, the field effect transistor FET converts an impedance of the electrical signal received therein and applies the resultant signal to the non-inverting terminal (+) of the amplifier A1. Since the amplifier A1 is connected to resistors R1 and R2 and capacitors C4 and C5, it serves to amplify and filter the output signal from the transistor FET. The resultant signal from the amplifier A1 is applied to the amplifier A2. Since the amplifier A2 is connected to resistors R3 and R4 and capacitors C6 and C7, it serves to amplify and filter the output signal from the amplifier A1.
Where the sensing unit 20 is subjected to an external vibration upon generating an output signal therefrom,: a vibration noise may be included in the output signal of the sensing unit 20 due to the piezo-electric characteristic of the ferroelectric element.
In the dual type infrared sensor, however, one of two infrared sensor elements is used as a reference element. This reference element is not exposed to any infrared rays. Accordingly, the vibration noise of the infrared sensor element caused by the external vibration is compensated by the reference voltage of the reference element.
Generally, noise includes thermal noise, shot noise and 1/f noise.
The thermal noise is generated due to the resistance component present in the circuit. This thermal noise can be processed by a differential amplifier circuit for amplifying a difference between the output signal of the sensor element and the output signal of the reference element.
Therefore, the dual type unit infrared sensor can detect a difference between infrared energies respectively incident on the sensor element and the reference element without responding to factors generating an erroneous operation such as vibration.
In other words, the infrared sensor can sense a variation in amount of infrared ray incident thereon because the pyroelectric element varies in temperature depending on the variation in amount of infrared rays and thereby generates a charge. Accordingly, the infrared sensor can detect an infrared ray source such as a human body moving within a field of view.
On the other hand, a pyroelectric infrared charge coupled device (IR-CCD) is shown in FIG. 5. As shown in FIG. 5, the pyroelectric IR-CCD includes a pyroelectric element 13 made of a single crystal such as LiTaO.sub.3 and provided with upper and lower electrodes 14 and 15. The lower electrode 15 is electrically connected to a gate electrode of the IR-CCD formed on a silicon substrate 16 by an indium bump.
Referring to FIG. 6, there is illustrated a pyroelectric infrared array sensor using such a pyroelectric IR-CCD. As shown in FIG. 6, the pyroelectric infrared array sensor includes a sensing unit 20 for convening an impedance upon sensing a motion of an object by its sensor element, a differential amplifier unit 21 for amplifying a difference between sensed data from the sensing unit 20 and a reference voltage of the reference element of the sensing unit 20, a sample/hold unit 22 for sampling/holding an output from the differential amplifier unit 21, an analog/digital converter unit 23 for converting an output signal from the sample/hold unit 22 into a digital signal, a microcomputer 24 for receiving an output from the analog/digital converter unit 23 and analyzing an infrared image signal on the basis of the received signal, and a control unit 25 for controlling the units of the pyroelectric infrared array sensor.
As infrared rays emitted from an object are projected onto infrared array elements of the sensing unit 20 via expensive lenses made of Ge or ZnSe, the infrared array applies pyroelectric current to the IR-CCD which, in turn, outputs an electrical signal.
Accordingly, an infrared image can be analyzed for motion of the object by the circuits connected to the downstream-side of the IR-CCD.
Although the overall system of the conventional unit infrared sensor has a simple and inexpensive construction capable of sensing a human body and an amount of motion of the human body, it can not sense the orientation of the human body.
On the other hand, the conventional infrared array sensor can also sense all information such as the orientation and position of the human body. However, this sensor has a problem that it is unsuitable to be applied to products such as an air conditioner because it is very expensive due to requirements of expensive lenses and complex signal processing procedures.